Oceana Gold Waihi North Project Waihi North Project Geochemical Assessment – Geochemistry of Tailings and Overburden, Treatment and Mitigation Revision 0 – 17-Jun-2022 Prepared for – Oceana Gold (New Zealand) Limited – Co No.: 2274246 58 AECOM factors not being applied to the laboratory / field tests; and use of Mean and 95% UCL data to calculate applicable limestone dosing rates. Ore geochemical testing on GOP and WUG ore material was found to exhibit generally similar geochemical characteristics to that of the existing ore material with the exception of mercury, which was found to be elevated in the Gladstone ore. The analytical results of the Leach Tests and SPLP analysis of the Gladstone ore material combined with the geochemical modelling undertaken suggest that arsenic, calcium, cadmium, cobalt, chromium, copper, iron, mercury, magnesium, nickel and lead concentrations in porewater will be reduced via adsorption to hydrous ferric oxides, while potassium, sodium and sulphate will not be significantly altered. The resultant predicted leachate water quality will be similar in nature to that monitored at the existing TSF facilities, with potentially less mixing with groundwater due to the presence of a geomembrane in some areas of the basal structure.
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